Progressive addition lenses

ABSTRACT

The present provides progressive addition lens designs and lenses in which unwanted lens astigmatism is reduced as compared to conventional progressive addition lenses. The lenses of the invention containing at least one surface that is a composite of a progressive surface design and a regressive surface design.

FIELD OF THE INVENTION

The present invention relates to multifocal ophthalmic lenses. Inparticular, the invention provides progressive addition lens designs andlenses in which unwanted lens astigmatism is reduced as compared toconventional progressive addition lenses.

BACKGROUND OF THE INVENTION

The use of ophthalmic lenses for the correction of ametropia is wellknown. For example, multifocal lenses, such as progressive additionlenses (“PAL's”), are used for the treatment of presbyopia. Theprogressive surface of a PAL provides far, intermediate, and near visionin a gradual, continuous progression of vertically increasing dioptricpower from far to near focus, or top to bottom of the lens.

PAL's are appealing to the wearer because PAL's are free of the visibleledges between the zones of differing dioptric power that are found inother multifocal lenses, such as bifocals and trifocals. However, aninherent disadvantage in PAL's is unwanted astigmatism, or astigmatismintroduced or caused by one or more of the lens' surfaces. In harddesign PAL's, the unwanted astigmatism borders the lens channel and nearvision zone. In soft design PAL's, the unwanted astigmatism extends intothe distance vision zone. Generally, in both designs the unwanted lensastigmatism at or near its approximate center reaches a maximum thatcorresponds approximately to the near vision dioptric add power of thelens.

Many PAL designs are known that attempt to reduce unwanted astigmatismwith varying success. One such design is disclosed in U.S. Pat. No.5,726,734 and uses a composite design that is computed by combining thesag values of a hard and a soft PAL design. The design disclosed in thispatent is such that the maximum, localized unwanted astigmatism for thecomposite design is the sum of the contributions of the hard and softdesigns areas of maximum, localized unwanted astigmatism. Due to this,the reduction in the maximum, localized unwanted astigmatism that may berealized by this design is limited. Therefore, a need exists for adesign that permits even greater reductions of maximum, localizedunwanted astigmatism than in prior art designs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of the distortion area of a progressive lens.

FIG. 2a is a cylinder contour of the progressive surface used in thelens of Example 1.

FIG. 2b is a power contour of the progressive surface used in the lensof Example 1.

FIG. 3a is a cylinder map of the regressive surface used in the lens ofExample 1.

FIG. 3b is a power map of the regressive surface used in the lens ofExample 1.

FIG. 4a is a cylinder contour of the composite surface of Example 1.

FIG. 4b is the power contour of the composite surface of Example 1.

FIG. 5 is the cylinder contour of the concave progressive surface ofExample 2.

FIG. 6a is the cylinder contour of the lens of Example 2.

FIG. 6b is the power contour of the lens of Example 2.

FIG. 7a is the cylinder contour of a conventional lens.

FIG. 7b is the power contour of a conventional lens.

FIG. 8 is the cylinder contour of the concave progressive additionsurface of the lens of Example 3.

FIG. 9a is the cylinder contour of the lens of Example 3.

FIG. 9b is the power contour of the lens of Example 3.

DESCRIPTION OF THE INVENTION AND ITS PREFERRED EMBODIMENTS

In the present invention, a composite surface is formed by combining thedesigns of a progressive and a regressive surface. It is a discovery ofthe invention that progressive lenses with reduced unwanted astigmatismmay be constructed by combining progressive addition and regressivesurfaces into a composite surface.

In one embodiment, the invention provides a method for designing aprogressive addition surface comprising, consisting of, and consistingessentially of: a.) designing a progressive surface having at least onefirst area of unwanted astigmatism; b.) designing a regressive surfacehaving at least one second area of unwanted astigmatism; and c.)combining the progressive surface and regressive surface designs to forma composite progressive surface design, wherein the at least one firstand second areas of unwanted astigmatism are aligned. In anotherembodiment, the invention provides a progressive addition lenscomprising, consisting essentially of, and consisting of a surface ofthe composite surface design produced by this method.

By “lens” or “lenses” is meant any ophthalmic lens including, withoutlimitation, spectacle lenses, contact lenses, intraocular lenses and thelike. Preferably, the lens of the invention is a spectacle lens.

By “progressive addition surface” is meant a continuous, asphericsurface having distance and near viewing or vision zones, and a zone ofincreasing dioptric power connecting the distance and near zones. Oneordinarily skilled in the art will recognize that, if the progressivesurface is the convex surface of the lens, the distance vision zonecurvature will be less than that of the near zone curvature and if theprogressive surface is the lens' concave surface, the distance curvaturewill be greater than that of the near zone.

By “area of unwanted astigmatism” is meant an area on the lens surfacehaving about 0.25 diopters or more of unwanted astigmatism.

By “regressive surface” is meant a continuous, aspheric surface havingzones for distance and near viewing or vision, and a zone of decreasingdioptric power connecting the distance and near zones. If the regressivesurface is the convex surface of the lens, the distance vision zonecurvature will be greater than that of the near zone and if theregressive surface is the lens' concave surface, the distance curvaturewill be less than that of the near zone.

By “aligned” in relation to the areas of unwanted astigmatism is meantthat the areas of unwanted astigmatism are disposed so that there ispartial or substantially total superposition or coincidence when thesurface are combined to form the composite surface.

A number of optical parameters conventionally are used to define andoptimize a progressive design. These parameters include areas ofunwanted astigmatism, areas of maximum, localized unwanted astigmatism,channel length and width, distance and reading zone widths, readingpower width, and normalized lens distortion. Normalized lens distortionis the integrated, unwanted astigmatism of the lens below the opticalcenter, primary reference point, divided by the dioptric add power ofthe lens. Referring to FIG. 1, for progressive addition lenses, thenormalized lens distortion, D_(L) can be calculated by the equation:

D _(L) =M _(A)/(3A _(p)){A _(L)/2−A _(I) −πN _(W) ²/4}  (I)

wherein: A_(L) is the lens area; N_(W) is the near width; M_(A) is themaximum; localized, unwanted astigmatism (the highest, measurable levelof astigmatism in an area of unwanted astigmatism on a lens surface);and A_(p) is the dioptric power of the lens at y=−20 mm below theprimary reference point. A_(I) is the area of the intermediate zonewhere the unwanted astigmatism is less than 0.5 diopters and iscalculated by the equation:

A _(I) =I _(L)/2[I _(W) +D _(W)]+(C _(L) −I _(L))/2[I _(W) +N_(W)]  (II)

where: I_(W) is width of the intermediate zone where the unwantedastigmatism is less than 0.5 diopters; D_(W) and N_(W) are the widths ofthe distance (at y=0) and near (at y=−20 mm) viewing zones,respectively, where the unwanted astigmatism is less than about 0.5diopters; C_(L) is the channel length; and I_(L) is the length along thecenter of the channel between the prism reference point and thenarrowest width in the intermediate zone.

For purposes of Equation II, the near width and intermediate widths arenot synonymous with reading and channel width. Rather, whereas readingand channel width are defined based on clinically relevant threshold forgood vision, the near and intermediate widths of Equation II are basedon a 0.5 diopter astigmatic threshold.

In the lenses of the invention, the normalized lens distortion issignificantly reduced compared to conventional progressive additionlenses. Thus, in a preferred embodiment, the invention providesprogressive addition lenses comprising, consisting essentially of, andconsisting of at least one progressive addition surface having anormalized lens distortion of less than about 300.

In the lenses of the invention, the dioptric add power, or the amount ofdioptric power difference between the distance and near vision zones, ofthe progressive surface design is a positive value and that of theregressive surface design, a negative value. Thus, because the add powerof the composite surface is the sum of the progressive and regressivesurface designs' dioptric add powers, the regressive surface design actsto subtract dioptric add power from the progressive surface design.

It is known that a progressive addition surface produces unwantedastigmatism at certain areas on the surface. The unwanted astigmatism ofan area may be considered a vector quantity with a magnitude and axis oforientation that depends, in part, on the location of the astigmatism onthe surface. A regressive surface also has areas of unwantedastigmatism, the magnitude and axis of the regressive surfaceastigmatism are determined by the same factors that are determinativefor the progressive surface astigmatism. However, the axis of theregressive surface astigmatism typically is orthogonal to that of theprogressive surface astigmatism. Alternately, the magnitude of theregressive surface astigmatism may be considered to be opposite in signto that of the progressive surface astigmatism at the same axis.

Thus, combining a progressive surface design with an area of unwantedastigmatism with a regressive surface design with a comparably locatedarea of unwanted astigmatism reduces the total unwanted astigmatism forthat area when the two designs are combined to form a composite surfaceof a lens. The reason for this is that the unwanted astigmatism of thelens at a given location will be the vector sums of the unwantedastigmatisms of the progressive and regressive surface designs. Becausethe magnitudes of the progressive addition and regressive surfacedesigns' astigmatisms have opposite signs, a reduction in the totalunwanted astigmatism of the composite surface is achieved. Although theaxis of orientation of the unwanted astigmatism of the regressivesurface design need not be the same as that at a comparable location onthe progressive surface design, preferably the axes are substantiallythe same so as to maximize the reduction of unwanted astigmatism.

At least one area of astigmatism of the progressive surface design mustbe aligned with one area of astigmatism of the regressive surface designto achieve a reduction of unwanted astigmatism in the composite surface.Preferably, the areas of maximum, localized unwanted astigmatism, or theareas of highest, measurable unwanted astigmatism, of each of thesurface designs are aligned. More preferably, all areas of unwantedastigmatism of one surface design are aligned with those of the other.

In another embodiment, the surfaces' distance and near zones, as well asthe channels are aligned. By aligning the surfaces in such a manner, oneor more areas of unwanted astigmatism of the progressive surface designwill overlap with one or more such areas on the regressive surfacedesign. In another embodiment, the invention provides a surface of alens comprising, consisting essentially of, and consisting of one ormore progressive addition surface designs and one or more regressivesurface designs, wherein the distance vision zones, near vision zonesand channels of the progressive and regressive surface designs aresubstantially aligned.

In the lenses of the invention, the composite surface may be on theconvex, concave, or both surfaces of the lens or in layers between thesesurfaces. In a preferred embodiment, the composite surface forms theconvex lens surface. One or more progressive addition and regressivesurface designs may be used in the composite surface, but preferablyonly one of each surface is used. In embodiments in which a compositesurface is the interface layer between the concave and convex surfaces,preferably the materials used for the composite surface is of arefractive index that differs at least about 0.01, preferably at least0.05, more preferably at least about 0.1.

One ordinarily skilled in the art will recognize that the progressiveaddition and regressive surface designs useful in the invention may beeither of a hard or soft design type. By hard design is meant a surfacedesign in which the unwanted astigmatism is concentrated below thesurface's optical centers and in the zones bordering the channel. A softdesign is a surface design in which the unwanted astigmatism is extendedinto the lateral portions of the distance vision zone. One ordinarilyskilled in the art will recognize that, for a given dioptric add power,the magnitude of the unwanted astigmatism of a hard design will begreater than that of a soft design because the unwanted astigmatism ofthe soft design is distributed over a wider area of the lens.

In the lens of the invention, preferably, the progressive additionsurface designs are of a soft design and the regressive surface designsare of a hard design. Thus, in yet another embodiment, the inventionprovides a lens surface comprising, consisting essentially of, andconsisting of a one or more progressive addition surface designs and oneor more regressive surface designs, wherein the one or more progressiveaddition surface designs are soft designs and the one or more regressivesurface designs are hard designs. More preferably, the progressiveaddition surface design has a maximum unwanted astigmatism that is lessin absolute magnitude than the surfaces' dioptric add power and, for theregressive surface design, is greater in absolute magnitude.

The composite progressive surface of the invention is provided by firstdesigning a progressive addition and a regressive surface. Each of thesurfaces is designed so that, when combined with the design of the othersurface or surfaces to form the composite progressive surface,substantially all of the areas of maximum, localized unwantedastigmatism are aligned. Preferably, each surface is designed so thatthe maxima of the unwanted astigmatism areas are aligned and when thesurfaces' designs are combined to obtain the composite surface design,the composite surface exhibits maximum, localized unwanted astigmatismthat is at least less than about 0.125 diopters, preferably less thanabout 0.25 diopters, than the sum of absolute value of the maxima of thecombined surfaces.

More preferably, each of the progressive and regressive surfaces isdesigned so that, when combined to form the composite surface, thecomposite surface has more than one area of maximum, localized unwantedastigmatism on each side of the composite surface's channel. This use ofmultiple maxima further decreases the magnitude of the areas of unwantedastigmatism on the composite surface. In a more preferred embodiment,the areas of maximum, localized unwanted astigmatism of the compositesurface form plateaus. In a most preferred embodiment, the compositesurface has more than one area of maximum, localized unwantedastigmatism in the form of plateaus on each side of the compositesurface's channel.

Designing of the progressive and regressive surfaces used to form thecomposite surface design is within the skill of one of ordinary skill inthe art using any number of known design methods and weightingfunctions. Preferably, however, the surfaces are designed using a designmethod that divides the surface into a number of sections and provides acurved-surface equation for each area as, for example, is disclosed inU.S. Pat. No. 5,886,766, incorporated herein in its entirety byreference.

The surface designs useful in the lenses of the invention may beprovided by using any known method for designing progressive andregressive surfaces. For example, commercially available ray tracingsoftware may be used to design the surfaces. Additionally, optimizationof the surfaces may be carried out by any known method.

In optimizing the designs of the individual surfaces or the compositesurface, any optical property may be used to drive the optimization. Ina preferred method, the near vision zone width, defined by the constancyof the spherical or equivalent spherocylindrical power in the nearvision zone may be used. In another preferred method, the magnitude andlocation of the peaks or plateaus of the maximum, localized unwantedastigmatism may be used. Preferably, for purposes of this method, thelocation of the peaks and plateaus is set outside of a circle having anorigin at x=0, y=0, or the fitting point, as its center and a radius of15 mm. More preferably, the x coordinate of the peak is such that |x|>12and the y<−12 mm.

Optimization may be carried out by any convenient method known in theart. Additional properties of a specific lens wearer may be introducedinto the design optimization process, including, without limitation,variations in pupil diameter of about 1.5 to about 5 mm, imageconvergence at a point about 25 to about 28 mm behind the front vertexof the surface, pantoscopic tilt of about 7 to about 20 degrees, and thelike, and combinations thereof.

The progressive and regressive surface designs used to form thecomposite progressive surface may be expressed in any of a variety ofmanners, including and preferably as sag departures from a basecurvature, which may be either a concave or convex curvature.Preferably, the surfaces are combined on a one-to-one basis meaning thatthe sag value Z₁ at point (x, y) of a first surface is added to the sagvalue Z₂ at the same point (x, y) on a second surface. By “sag” is meantthe absolute magnitude of the z axis distance between a point on aprogressive surface located at coordinates (x, y) and a point located atthe same coordinates on a reference, spherical surface of the samedistance power.

More specifically in this embodiment, following designing and optimizingof each surface, the sag values of the surfaces are summed to obtain thecomposite surface design, the summation performed according to thefollowing equation:

Z(x, y)=Σa _(i) Z _(i)(x, y)  (III)

wherein Z is the composite surface sag value departure from a basecurvature at point (x, y), Z_(i) is the sag departure for the ithsurface to be combined at point (x, y) and a_(i) are coefficients usedto multiply each sag table. Each of the coefficients may be of a valuebetween about −10 and about +10, preferably between about −5 to about+5, more preferably between about −2 and about +2. The coefficients maybe chosen so as to convert the coefficient of highest value to about +or −1, the other coefficients being scaled appropriately to be less thanthat value.

It is critical to perform the sag value summation using the samecoordinates for each surface so that the distance and near powersdesired for the composite surface are obtained. Additionally, thesummation must be performed so that no unprescribed prism is inducedinto the composite surface. Thus, the sag values must be added from thecoordinates of each surface using the appropriate coordinate systems andorigins. Preferably, the origin from which the coordinate system isbased will be the prism reference point of the surface, or the point ofleast prism. It is preferable to calculate the sag values of one surfacerelative to the other along a set of meridians by a constant or avariable magnitude before performing the summation operation. Thecalculation may be along the x-y plane, along a spherical or asphericalbase curve, or along any line on the x-y plane. Alternatively, thecalculation may be a combination of angular and linear displacements tointroduce prism into the lens.

The distance and near vision powers for the progressive and regressivesurface designs are selected so that, when the designs are combined toform the composite surface, the powers of the lens are those needed tocorrect the wearer's visual acuity. The dioptric add power for theprogressive addition surface designs used in the invention eachindependently may be about +0.01 to about +6.00 diopters, preferablyabout +1.00 diopters to about +5.00 diopters, and more preferably about+2.00 diopters to about +4.00 diopters. The dioptric add power of theregressive surface designs are each independently may be about −0.01 toabout −6.00, preferably about −0.25 to about −3.00 diopters, and morepreferably about −0.50 to about −2.00 diopters.

In the case in which more than one composite progressive surface is usedto form the lens, or the composite surface used in combination with oneor more progressive surface, the dioptric add power of each of thesurfaces is selected so that the combination of their dioptric addpowers results in a value substantially equal to the value needed tocorrect the lens wearer's near vision acuity. The dioptric add power ofeach of the surfaces may be from about +0.01 diopters to about +3.00diopters, preferably from about +0.50 diopters to about +5.00 diopters,more preferably about +1.00 to about +4.00 diopters. Similarly, thedistance and near dioptric powers for each surface are selected so thatthe sum of the powers is the value needed to correct the wearer'sdistance and near vision. Generally, the distance curvature for eachsurface will be within the range of about 0.25 diopters to about 8.50diopters. Preferably, the curvature of the distance zone of a concavesurface may be about 2.00 to about 5.50 diopters and for a convexsurface, about 0.5 to about 8.00 diopters. The near vision curvature foreach of the surfaces will be about 1.00 diopters to about 12.00diopters.

Other surfaces, such as spheric, toric, aspheric and atoric surfaces,designed to adapt the lens to the ophthalmic prescription of the lens'wearer may be used in combination with, or in addition to, the compositeprogressive addition surface. Additionally, the individual surfaces eachmay have a spherical or aspherical distance vision zone. The channel, orcorridor of vision free of unwanted astigmatism of about 0.75 or greaterwhen the eye is scanning from the distance to the near zone and back,may be short or long. The maximum, localized unwanted astigmatism may becloser to the distance or near viewing zone. Further, combinations ofany of the above variations may be used.

In a preferred embodiment, the lens of the invention has a convexcomposite and concave progressive addition surfaces. The convexcomposite surface may be a symmetric or asymmetric soft design with anaspherical distance viewing zone and a channel length of about 10 toabout 20 mm. The maximum, localized unwanted astigmatism is locatedcloser to the distance than the near viewing zone and preferably is oneither side of the channel. More preferably, the maximum, localizedunwanted astigmatism is superior to the point on the surface at whichthe dioptric add power of the surface's channel reaches about 50 percentof the surface's dioptric add power. The distance viewing zone isaspherized to provide additional plus power to the surface of up toabout 2.00 diopters, preferably up to about 1.00 diopters, morepreferably up to about 0.50 diopters. Aspherization may be outside of acircle centered at the fitting point and having a radius of about 10 mm,preferably about 15 mm, more preferably about 20 mm.

The concave progressive surface of this embodiment is an asymmetrical,and preferably an asymmetrical, hard design, with a spherical distanceviewing zone and channel length of about 12 to about 22 mm. The distanceviewing zone is designed to provide additional plus power of less thanabout 0.50 diopters, preferably less than about 0.25 diopters. Themaximum, localized unwanted astigmatism is located closer to the nearviewing zone, preferably on either side of the lower tow-thirds of thechannel.

In yet another embodiment, the lens of the invention has a convexcomposite surface and concave regressive surface. In still anotherembodiment, the lens has a convex composite surface, a regressivesurface as an intermediate layer, and a spherocylindrical concavesurface. In yet another embodiment, the convex surface is the compositesurface, a regressive surface is an intermediate layer and the concavesurface is a conventional progressive addition surface. In allembodiments it is critical that the distance, intermediate and nearviewing areas of all surfaces align so as to be free of unwantedastigmatism.

The lenses of the invention may be constructed of any known materialsuitable for production of ophthalmic lenses. Such materials are eithercommercially available or methods for their production are known.Further, the lenses may be produced by any conventional lens fabricationtechnique including, without limitation grinding, whole lens casting,molding, thermoforming, laminating, surface casting, or combinationsthereof. Preferably, the lens is fabricated by first producing anoptical preform, or lens with a regressive surface. The preform may beproduced by any convenient means including, without limitation injectionor injection-compression molding, thermoforming, or casting.Subsequently, at least one progressive surface is cast onto the preform.Casting may be carried out by any means but preferably is performed bysurface casting including, without limitation, as disclosed in U.S. Pat.Nos. 5,147,585, 5,178,800, 5,219,497, 5,316,702, 5,358,672, 5,480,600,5,512,371, 5,531,940, 5,702,819, and 5,793,465 incorporated herein intheir entireties by reference.

The invention will be clarified further by a consideration of thefollowing, non-limiting examples.

EXAMPLES Example 1

A soft design, convex progressive addition surface was produced as a sagtable wherein Z₁ denoted the sag value departure from a base curvatureof 5.23 diopters for the distance zone. In FIGS. 2a and 2 b are depictedthe cylinder and power contours for this surface. The add power was 1.79diopters with a channel length of 13.3 mm and maximum, localized,unwanted astigmatism of 1.45 diopters at x=−8 mm and y=−8 mm. The prismreference point used was x=0 and y=0 and the refractive index (“RI”) was1.56.

A hard design regressive surface design was produced for a convexsurface as a sag table wherein Z₂ denoted the sag value departure from abase curvature of 5.22 diopters for the distance zone. In FIGS. 3a and 3b are depicted the cylinder and power contours for this surface. The addpower was −0.53 diopter, the channel length was 10.2 mm and the maximum,localized unwanted astigmatism was 0.71 diopters at x=−10 mm and y=−10mm. The prism reference point used was x=0 and y=0 and the RI was 1.56.

A convex composite surface design was produced using Equation IIIwherein a₁=a₂=1 to generate the sag value departures. In FIGS. 4a and 4b are depicted the cylinder and power contours for the compositesurface, which surface has a base curvature of 5.23 diopters and an addpower of 1.28 diopters. The composite surface contains a single maximum,localized unwanted astigmatism area located on either side of thechannel. The magnitude of this astigmatism maximum was 0.87 diopters andthe channel length is 13.0 mm. The composite surface's area ofastigmatism was located at x=−10 mm and y=−18 mm. The maximumastigmatism and normalized distortion of the composite surface wassignificantly lower, without compromise of the other optical parameters,than that of comparable dioptric add power prior art lenses. Forexample, a Varilux COMFORT® lens has a maximum astigmatism value andnormalized distortion of 1.41 diopters and 361, respectively for a 1.25diopter add power as shown in Table 2. For a composite surface lens themaximum astigmatism is 0.87 diopters and the normalized lens distortionof the lens is calculated to be 265.

Example 2

A concave progressive addition surface was designed using a materialrefractive index of 1.573, a base curvature of 5.36 diopters and an addpower of 0.75 diopters. FIG. 5 depicts the cylinder contours of thissurface. The maximum, localized astigmatism was 0.66 diopters at x=−16mm and y=−9 mm. The prism reference point used was at x=0 and y=0.

This concave surface was combined with the convex composite surface fromExample 1 to form a lens with a distance power of 0.08 diopters and anadd power of 2.00 diopters. In the Table is listed the key opticalparameters of this lens (Example 2), and in FIGS. 6a and 6 b is depictedthe cylinder and power contours. The maximum astigmatism is 1.36diopters, significantly lower than prior art lenses shown in the Table 1as Varilux COMFORT® (Prior Art Lens 1 and FIGS. 7a and 7 b. Thenormalized lens distortion of the lens is calculated to be 287,significantly less than the prior art lenses of Table 3. Additionally,none of the other optical parameters are compromised.

Example 3

In order to demonstrate the capability of the design approach of theinvention to optimize specific optical parameters, specifically thereading power width, a concave progressive addition surface was designedusing a material RI of 1.573, a base curvature of 5.4 diopters and anadd power of 0.75 diopters. In FIG. 8 is depicted the cylinder contourof this surface. The maximum, localized astigmatism was 0.51 diopters atx=−15 mm and y=−9 mm. The prism reference point used was at x=0 and y=0.

This concave surface was combined with the convex composite surface fromExample 1 to form a lens with a distance power of 0.05 diopters and anadd power of 2.00 diopters. In the Table is listed the key opticalparameters of this lens (Example 3), and in FIGS. 9a and 9 b is shownthe cylinder and power contours. The maximum astigmatism is 1.37diopters, significantly lower than the prior art lens shown in Table 1as Varilux COMFORT®—(Prior Art Lens 1 and FIGS. 7a and 7 b. Thenormalized lens distortion of the lens is calculated to be 289, which issignificantly less than the prior art lenses of Table 3. The lowerastigmatism of the concave surface smoothens out the astigmatic contoursand increases the reading power width from 7.4 mm to 8.6 mm. None of theother optical parameters are compromised.

TABLE 1 Prior Art Optical Parameter Lens 1 Example 2 Example 3 DistancePower (D) 0.00 0.00 0.00 Add Power (D) 1.99 2.01 2.01 Distance Width(mm) 13.5 12.6 12.6 Reading Width (mm) 17.6 14.6 15.2 Reading PowerWidth (mm) 13.9 7.4 8.6 Channel Length (mm) 12.2 12.4 12.2 Channel Width(mm) 6.3 8.9 8.8 Max. Astig. Location (x,y in deg.) 16.8-12.1 12.5-14.911.3-11.1 Max. Astigmatism (D) 2.46 1.36 1.37

TABLE 2 Varilux COMFORT ® Example 1 Label Add power (D) 1.25 1.25 A_(P)(D) 1.40 1.28 D_(W) (mm) 45.65 30.00 I_(W) (mm) 5.00 5.32 N_(W) (mm)7.50 9.27 I_(L) (mm) 11.25 8.00 Channel Length (mm) 12.85 13.00 M_(A)(D) 1.41 0.87 Distortion Area (mm²) 1075 1168 D_(L) 361 265

TABLE 3 Rodenstock Varilux MULTI- Zeiss Hoya Varilux Sola COMFORT ®GRESSIV ® GRADAL ® EX ® PANAMIC ® PERCEPTA ® Example 2 Example 3 LabelAdd Power 2.00 2.00 2.00 2.00 2.00 2.00 2.00 2.00 (D) A_(P) (D) 1.992.11 2.21 2.28 2.19 2.12 2.01 2.01 D_(W) (mm) 13.50 10.20 14.45 13.0510.25 14.20 12.60 12.60 I_(W) (mm) 3.00 4.00 3.75 4.00 6.50 2.75 3.504.00 N_(W) (mm) 10.00 10.00 5.50 6.00 14.90 11.50 8.00 8.00 I_(L) (mm)8.75 8.75 10.00 12.50 8.75 8.75 8.75 8.75 Channel Length 12.20 12.4512.90 13.05 12.20 12.50 12.40 12.20 (mm) M_(A) (D) 2.46 2.56 2.20 2.452.25 2.53 1.36 1.37 Distortion Area 1241 1246 1286 1276 1129 1209 12721270 (mm²) D_(L) 511 504 427 457 387 481 287 289

What is claimed is:
 1. A progressive addition lens, comprising anormalized lens distortion of less than about 300 mm² and comprising afront surface and back surface of the lens wherein at least one of thefront and back surfaces.
 2. The lens of claim 1, wherein the compositesurface exhibits a maximum, localized unwanted astigmatism that is about0.125 diopters less than the sum of an absolute value of the maximum,localized astigmatism of each of the progressive and regressivesurfaces.
 3. The lens of claim 1 or 2, further comprising a secondprogressive addition surface.
 4. The lens of claim 1 or 2, furthercomprising a second surface that is a regressive surface.